Ultraviolet light with wavelengths of 150 to 250 nm, which is emitted by deuterium lamps, KrF excimer lasers, ArF excimer lasers, and F2 excimer lasers, has been increasingly used in the field of micromachining such as photolithography and laser machining and in medical fields, such as for sterilization and disinfection. Accordingly, optical fibers for transmitting ultraviolet light have been researched and developed as a medium for transmitting the ultraviolet light with such wavelengths. Unfortunately, transmission of ultraviolet light deteriorates the glass and increases its transmission loss. Silica glass optical fibers, although having excellent ultraviolet resistance characteristics, are unsatisfactory. The increase in the transmission loss of the silica glass optical fibers in the ultraviolet region is considered to be due to optical absorption caused by defects which the irradiation of the ultraviolet light causes in the silica glass. Consequently, methods of compensating for these defects with hydrogen atoms have been employed to improve the ultraviolet resistance characteristics.
Japanese Unexamined Patent Application Publication No. 6-034830 (Ref. 1) discloses a structure such that an optical fiber having a pure quartz core and a fluorine-doped quartz cladding is accommodated in a stainless steel (SUS) pipe, in which a high-pressure hydrogen gas atmosphere of 5 to 10 kg/cm2 is kept at a high temperature of 100° C. to 150° C. by covering the outside of the SUS pipe with a heating member so that the optical fiber is exposed to the hot, high-pressure hydrogen atmosphere during or after transmission of the ultraviolet light.
Japanese Unexamined Patent Application Publication No. 6-056457 (Ref. 2) discloses a method of manufacturing an optical fiber, which is characterized in that an optical fiber drawn from a preform consisting of a pure quartz core and a fluorine-doped quartz cladding is exposed to a hydrogen atmosphere upon drawing from the preform while the optical fiber has a high temperature or to a hot hydrogen atmosphere so as to diffuse a large amount of hydrogen into the optical fiber.
Japanese Unexamined Patent Application Publication Nos. 11-029335 (Ref. 3) and 10-316445 (Ref 4) disclose a glass product and its manufacturing method, in which a quartz glass product is irradiated with electromagnetic waves to cause defects in glass and the glass product is then kept in a hydrogen atmosphere so as to substantially prevent the occurrence of an increase in optical absorption in the ultraviolet region.
Japanese Unexamined Patent Application Publication No. 2000-214336 (Ref. 5) discloses a quartz glass optical fiber in which microparticles that can store hydrogen are provided over a cladding in dispersedly distributed manner.
Japanese Unexamined Patent Application Publication No. 2000-214336 (Ref. 5) discloses a quartz glass optical fiber in which microparticles that can store hydrogen are provided over a cladding in dispersedly distributed manner. The method in Ref 1 unfortunately requires a large apparatus. The methods in Refs. 2, 3, and 4, although effective, gradually lose their effects with increasing defects caused by the ultraviolet light. These methods, therefore, are unsatisfactory for use in devices that emit strong ultraviolet light. In the method in Ref. 5, a sufficient amount of hydrogen-containing material, such as resins and hydrogen-absorbing alloys, is required to be enclosed corresponding to the volume of the optical fibers. Thus, this method is undesirable because a large container for an optical fiber bundle is required in the case where hundreds or thousands of optical fibers are bundled.
FIG. 8 shows a known optical fiber bundle 14 including loosely bundled optical fibers 11, a pipe 13 accommodating the optical fibers 11, and collets 12 holding the ends of the optical fibers 11. Referring to FIG. 9, the optical fiber bundle 14 is produced by drawing optical fibers from an optical fiber glass preform, then bundling and fixing the optical fibers at their ends (bundling), and finally accommodating the bundled optical fibers in a container. A method conceivable as a combination of such techniques as described above is such that a pipe accommodating an optical fiber bundle is filled with a hydrogen-containing atmosphere and completely sealed. This method, however, has a high risk of danger such as explosion because operations involving heat treatment such as welding and sealing must be carried out while the container is filled with a hydrogen-containing atmosphere.